1. Field of the Invention
This invention relates to a stator for a vehicle alternator, and relates in particular to the shape of the coil end portions of the stator windings inserted into the slots of the stator core.
2. Description of the Related Art
FIG. 7 is a perspective view showing a conventional stator for a vehicle alternator, FIG. 8 is a perspective view showing the stator windings removed from a conventional stator for a vehicle alternator, and FIG. 9 is a plan schematically showing an essential part of a conventional stator for a vehicle alternator.
In each figure, a stator 1 is composed of a stator core 2 made of laminated sheet steel formed with a plurality of slots 2a, and stator windings 3 inserted into the slots 2a formed in the stator core 2. When the alternator rotor has the usual six poles, there are thirty-six slots 2a in the stator core 2.
The coil strand is inserted into every third slot 2a around the core. When one round is completed, a second round is made inserting the coil strand into the same slots 2a, and this is repeated a certain number of times to form one phase of a winding 3 according to the concentrated winding method. In a similar way, the slots 2a into which coil strands are inserted are staggered to form three phases of stator windings 3. Each of the stator windings 3 is composed of straight portions 3a which are inserted into the slots 2a, and coil end portions 3b which connect adjacent straight portions 3a at the axial ends of the stator core 2.
One phase of stator winding 3 (external winding 3A) is wound around the radially outer edge of the stator core 2, another phase of stator winding 3 (internal winding 3B) is wound around the inner edge, and the remaining phase of winding 3 (intermediate winding 3C) is wound between the other two. The shaded portion in FIG. 8 represents the external winding 3A.
Next, a description will now be made of the coil end portion of the conventional stator winding 3.
As shown in FIG. 10, each of the coil strands 4 composing the stator windings 3 rises out of a slot 2a, then bends at nearly a right angle, extends circumferentially, bends at nearly a right angle at a point above the third slot 2a away, and descends into the latter slot 2a. As shown in FIGS. 11 and 12, as each of the coil strands 4 rises out of a slot 2a, it rises up such that it overlaps the previous strands in the radial direction, bends at a different height, and descends such that it overlaps the previous strands in the radial direction again. The internal winding 3B and intermediate winding 3C are shown in abbreviated form in FIG. 12.
As described in Japanese Patent No. 4-42899 (U.S. Pat. No. 4,857,787), in stator windings constructed in this manner, coil strands 4 are wound a certain number of times to form ring-shaped coil units, and the ring-shaped coil units are formed into star-shaped coil units having straight portions 3a and coil end portions 3b. Next, each of the straight portions 3a of the star-shaped coil units is inserted into each of the slots 2a and incorporated into the stator core 2. Then, the coil end portions 3b are reshaped to certain dimensions, as shown in FIG. 12, to ensure the integrity of the generator.
FIG. 13 is a side elevation showing the vicinity of the coil end portions in another conventional stator for a vehicle alternator, and FIG. 14 is a plan schematically showing an essential part of another conventional stator for a vehicle alternator. The above conventional example explained stator windings according to the concentrated winding method; the following example will explain stator windings according to the distributed winding method.
As described in Japanese Patent No. 4-42899, in this example coil strands 4 are wound a certain number of times to form ring-shaped coil units, and the ring-shaped coil units are formed into star-shaped coil units having straight portions 3a and coil end portions 3b. Next, the star-shaped coil units are divided into two sets of distributed coil units 5a, 5b, and one set of distributed coil units 5b is inverted 180.degree. and aligned with the other set of distributed coil units 5a and then each of the straight portions 3a is inserted into each of the slots 2a so that the stator windings are incorporated into the stator core 2. Then the coil end portions 3b are reshaped.
As shown in FIG. 14, in the stator windings 3 incorporated into the stator core 2 in this manner, the external winding 3A is wound around the radially outer edge of the stator core 2, the internal winding 3B is wound around the inner edge, and the intermediate winding 3C is wound between the other two.
As shown in FIG. 13, as each of the coil strands 4 of the distributed coil unit 5a composing each of the stator windings 3 rises out of a slot 2a, it rises up such that it overlaps the previous strands in the radial direction, then bends at nearly a right angle at a different height from the other strands, extends circumferentially in one direction, bends at nearly a right angle at a point above the third slot 2a away, and descends into the latter slot 2a. Also, as each of the coil strands 4 of the other distributed coil units 5b rises out of a slot 2a, it rises up such that it overlaps the previous strands in the radial direction, then bends at nearly a right angle at a different height from the other strands, extends circumferentially in the opposite direction, bends at nearly a right angle at a point above the third slot 2a away, and descends into the latter slot 2a.
The conventional stators for vehicle alternators arranged in the manner described above suffer from the following problems:
the position of the stator windings 3 of each phase is fixed concentrically at the outer edge, the inner edge, and between the other two, respectively, and so the coil end portions 3b of each phase line up radially and the radial dimension is enlarged; PA1 after the stator windings 3 are incorporated into the stator core 2, they are reshaped so that as each strand rises out of a slot 2a, it rises up such that it overlaps the previous strands in the radial direction, then bends at nearly a right angle at a different height from the other strands, extends circumferentially, bends at nearly a right angle at a point above the third slot 2a away, and descends into the latter slot 2a, and so the coil strands 4 at the coil end portions 3b are subjected to unnecessary bending, rubbing, and pressure, damaging the coil coatings and giving rise to poor insulation; and PA1 the coil end portions 3b of the stator windings 3 are not aligned, and so even if they are secured with varnish, poor conditions and the passage of time cause the external winding 3A and the internal winding 3B to both spread radially.
Also, Japanese Patent No. 4-24939 describes a conventional example in which the coil strands in each phase of the coil units are staggered and arranged and disposed flatly, and in which a gap is disposed between the coil units. In this conventional example, the thickness (radial dimension) of each phase of the coil units can be reduced to a certain extent, but because there is a gap disposed between the coil units, the radial dimension of the coil ends tends to increase. In addition, the coil strands in each phase of the coil units are not aligned, giving rise to poor insulation when each phase of the coil units is reshaped.
Japanese Patent Laid Open No. 61-185045 describes a conventional example in which the coil shape of each pole of each phase is identical to every other pole of every other phase. In this conventional example, the coil units are disposed such that the each unit is staggered axially, and so the coil end portions as a whole are higher and also spread radially, and the number of points at which the coil strands are bent is greater.